Known methods of forming a solidified granular material to be inserted into a tubular frame member for reinforcement include, for example, {circle around (1)} U.S. Pat. No. 4,610,836 “METHOD OF REINFORCING A STRUCTURAL MEMBER” (hereinafter referred to as Prior Art 1), {circle around (2)} art of solidifying granular materials with a resin material (hereinafter referred to as Prior Art 2), {circle around (3)} art of solidifying granular materials with a bridging liquid film (hereinafter referred to as Prior Art 3), and {circle around (4)} art of solidifying granular materials by themselves (hereinafter referred to as Prior Art 4).
In FIG. 2 of the official publication of Prior Art 1, there is disclosed a structure in which a frame member is filled with adhesive-coated glass microspheres which are enveloped with a fiberglass cloth. U.S. Pat. No. 4,695,343 also discloses a similar structure.
Prior Art 2 will be described with reference to FIGS. 13 and 14 hereof.
FIG. 13 illustrates a structural member 102 with a frame member 100 filled with a solidified granular material 101.
The solidified granular material 101 shown in FIG. 14 consists of granules 103 and a resin material 104 filled between the granules 103 to solidify the granules 103.
Prior Art 3 will be described with reference to FIG. 15.
A solidified granular material 110 shown in FIG. 15 has a structure in which adjacent granules 103 are bonded together with a bridging liquid film 111. The bonded structure is made by dampening the granules 103 with water or the like and then pressurizing and heating them to form the bridging liquid film 111, thereby forming the solidified granular material 110.
A solidified granular material 120 shown in FIG. 16 is made by surface-melting granules 103 to bond the granules 103 together. Reference numeral 121 denotes a solid portion of the surfaces of the granules 103 solidified after the melting.
The solidified granular material in Prior Art 1 forms a solid matter having high rigidity in its entirety because the microspheres are bonded together with the adhesive. However, when an impact is applied to the frame member, for example, small deformation of each microsphere significantly increases the load developed at the frame member, resulting in insufficient absorption of the impact energy.
In Prior Art 2, as shown in FIGS. 13 and 14, the granules 103 are solidified with the resin material 104 to increase the rigidity of the structural member 102. The increased amount of the resin material 104, however, increases the weight of the structural member 102.
In Prior Art 3, in FIG. 15, the bonding of the granules 103 using the bridging liquid film 111 depends on the surface tension, which provides small binding force, making it difficult to form a large solidified granular material 110.
In Prior Art 4, in FIG. 16, the solidification by the surface-melting of the granules 103 themselves provides strong connection between the adjacent granules 103. However, when the granules 103 are ceramics such as glass, silicon dioxide (SiO2) or aluminum oxide (Al2O3: alumina), it is necessary to heat the granules 103 at a very high temperature, requiring additional equipment such as a heating apparatus, and making it difficult to form a solidified granular material 120.
Further, in Prior Arts 1 to 4, to insert granules into a frame member after solidifying them, it is required to previously make the dimension of the solidified granular material match the inside dimension of the frame member using a solidification mold or the like. Thus, required is an additional production step of forming a solidified granular material.
Furthermore, even when granules are solidified after charged into a frame member, it can be difficult, depending on the shape of the frame member, to charge the granules into the frame member in close relationships, resulting in needless space therebetween.
It is thus required to allow a frame member charged with a solidified granular material to efficiently absorb a greater impact energy and to facilitate the formation of a solidified granular material of light weight and large size therein with no space therebetween without additional equipment and an additional production step.